Endocrine Physiology: Central Hormones Flashcards
Endocrine system includes
Hypothalamus Pituitary Thyroid Parathyroid Adrenals Pancreas Ovaries Testes
Chemical regulating system
Hormones = Made in glands or cells Transported by blood Distant target tissue receptors Activates physiological response
Hormone function
Control of = enzymatic reactions, transport of ions or molecules across cell membranes, gene expression and protein synthesis
Exert effects at very low concentrations
Bind to target cell receptors
Half-life indicates length of activity
Hormones control…
Water balance and blood volume Metabolism Energy balance and appetite Digestion Circulation Growth and development Reproduction RBC production Stress management
Tropic hormones
Act on other endocrine glands = control of hormone secretion
Non tropic hormones = act on effector organs
Hormones and neuropeptides
Endocrine glands =
Secrete hormones
Ductless
Neurohormones/neuropeptides
Neuro-secretory cells = secrete neurohormones or neuropeptides
Adrenal medulla = catecholamines
Hypothalamus = posterior pituitary
Hormones classification
Peptide hormones = protein
Steroid hormones = cholesterol
Amine hormones = tryptophan or tyrosine (amino acids)
Peptide or protein hormones
Prepohormone = large, inactive
Pro hormone = post-translational modification
Hormone = final cuts make before it exits the cell to make it an active hormone, travels freely in the blood but cannot cross cell membrane, short half-life
Peptide hormone-receptor complex
Surface receptor
Hormone binds = enzyme activation or opens channel or 2nd messenger systems
Cellular response
Steroid hormone features
Cholesterol derived = lipophilic and can enter target cell
Must travel in blood bound to a protein
Cytoplasmic or nuclear receptors (mostly) = activate DNA for protein synthesis
Slower acting
Longer half-life
Examples = cortisol, estrogen, testosterone
Amine hormone features
Ring structures
Derived from one of 2 amino acids
Tryptophan = melatonin
Tyrosine = thyroid hormones and catecholamines (epinephrine, norepinephrine, and dopamine)
Amine hormone structure
Catecholamines behave similar to peptides
Thyroid hormones behave similar to steroids
Synthesis and storage: peptide hormones
Made in advance
Stored in secretory vesicles
Synthesis and storage: steroid hormones
Synthesized on demand from precursors
Synthesis and storage: catecholamines
Made in advance
Stored in secretory vesicles
Synthesis and storage: thyroid hormones
Made in advance
Precursor stored in secretory vesicles
Release from parent cell: peptide hormones
Exocytosis
Release from parent cell: steroid hormones
Simple diffusion
Release from parent cell: catecholamines
Exocytosis
Release from parent cell: thyroid hormones
Simple diffusion
Transport in blood: peptide hormones
Dissolved in plasma
Transport in blood: steroid hormones
Bound to carrier proteins
Transport in blood: catecholamines
Dissolved in plasma
Transport in blood: thyroid hormones
Bound to carrier proteins
Half-life: peptide hormones
Short
Half-life: steroid hormones
Long
Half-life: catecholamines
Short
Half-life: thyroid hormones
Long
Location of receptor: peptide hormones
Cell membrane
Location of receptor: steroid hormones
Cytoplasm our nucleus
Some have membrane receptors also
Location of receptor: catecholamines
Cell membrane
Location of receptor: thyroid hormones
Nucleus
Response to receptor-ligand binding: peptide hormones
Activation of second messenger systems
May activate genes
Response to receptor-ligand binding: steroid hormones
Activation of genes for transcription and translation
May have nongenomic actions
Response to receptor-ligand binding: catecholamines
Activation of second messenger systems
Response to receptor-ligand binding: thyroid hormones
Activation of genes for transcription and translation
General target response: peptide hormones
Modification of existing proteins and induction of new protein synthesis
General target response: steroid hormones
Induction of new protein synthesis
General target response: catecholamines
Modification of existing proteins
General target response: thyroid hormones
Induction of new protein synthesis
Examples of peptide hormones
Insulin
Parathyroid hormone
Examples of steroid hormones
Estrogen
Androgens
Cortisol
Example of catecholamine proteins
Epinephrine
Norepinephrine
Example of thyroid hormone
Thyroxine (T4)
Blood hormone levels depend on
Rate of hormone secretion
Rate of hormone degradation
Rate of hormone excretion (kidneys)
Hormone interactions
Synergism = multiple stimuli (more than additive) eg) glucagon, epinephrine, cortisol Permissiveness = need second hormone to get full expression Anatgonsim = pairs of hormones with opposing effects eg) glucagon opposes insulin
Examples of permissiveness
One sided effect
TH increases number of receptor sites and increases effect of epinephrine
But epinephrine does not necessarily increase effect of TH
Negative feedback
Self regulates hormone levels
Turns off response homeostatically
Endocrine control
3 levels
Hypothalamic (from CNS)
Pituitary stimulation (hypothalamic tropic hormones)
Endocrine glands stimulation (pituitary tropic hormones)
Other factors
Hormone secretion also affected by: Emotional state Disease state Stress Diet Sleep Body cycles (cardiac rhythm, menstrual cycle)
Endocrine dysfunction
Abnormal plasma concentrations of a hormone
Hyposecretion = too little hormone is secreted
Hypersecretion = too much hormone is secreted
Hyposecretion
Primary hyposecretion = too little hormone is secreted due to gland abnormality
Causes = genetic (type 1 diabetes), dietary (iodine and TH), chemical or toxic, immunologic/auto-immune (hashimotos), diseases/cancer
Secondary hyposecretion = gland is normal but too little hormone is secreted due to decreased tropic hormone (anterior pituitary)
Hypersecretion
Causes = tumours (can continuously secrete excess hormone), immunologic
Primary hypersecretion = too much hormone is secreted due to abnormality within gland
Secondary hypersecretion = excessive stimulation from outside the gland causes over secretion
Hypothalamus
Homeostasis
Controls anterior pituitary which then controls other endocrine glands
Hypothalamic releasing and inhibiting hormones
Anterior pituitary hormones are stimulated or inhibited by one or more hypothalamic hormones
Posterior pituitary (neurohypophyis)
Hormones made in the hypothalamus
Oxytocin and ADH
Stored in the posterior pituitary
When neuron is excited hormone is released
Oxytocin
Stimulates uterine contractions in child birth
Promotes milk ejection during lactation
ADH (vasopressin)
Anti-diuretic hormone
Released if blood volume is low or blood osmolarity is high (eg-dehydration)
Increases water reabsorption in kidney (decreases urine output)
Diabetes insipidus
Decreased ADH
Excessive polyuria (urinating 8-90L of urine in 24 hours, hypotension, dizziness, constipation)
Treated with vasopressin replacements
Anterior pituitary (adenohypophysis)
Secretes 6 peptide hormones 5 are tropic FSH LH Growth hormone TSH Prolactin ACTH
Gonadotropins
FSH = follicle stimulating hormone, promotes sperm and egg production LH = luteinizing hormone, estrogen and testosterone secretion from gonads (acts with FSH), ovulation
Secreting hormones
TSH = thyroid stimulating hormone, acts on thyroid, promotes TH secretion ACTH = adenocorticopic hormone, acts on adrenal cortex, promotes cortisol secretion
Prolactin
Non-tropic hormone
Acts on mammary glands (breast development, milk production)
Growth hormone (GH)
Causes liver to release IGFs (insulin-like growth factors, somatomedins)
Stimulates protein synthesis and cell division (increased muscle, lengthening and thickening of bones)
Growth hormones other metabolic effects not related to growth
Increased fatty acids in blood (breakdown of fat stored in adipose tissue)
Increased blood glucose (decreased glucose uptake by muscles)
Endocrine control of growth
Growth depends on growth hormone and on other factors =
Genetics - maximum growth capacity
Adequate diet and sleep
Freedom from chronic disease and stress
Normal levels of growth-influencing hormones (TH, insulin, epinephrine, androgens)
Growth rate
Not continuous
Fetal growth (promoted by hormones from placenta, GH plays no role)
Postnatal growth spurt (first two years of life, GH controlled)
Pubertal growth spurt (adolescence, GH)
GH hyposecretion
Low GH
Dwarfism (no genetic disease)
Proportional growth
GH hypersecretion
Too much GH
Before growth plates close = gigantism, lengthening of bones
After growth plates close = acromegaly, thickening of bones instead
Pineal gland
Secretes melatonin = Influences body clock and antioxidant activity
Other roles need research = SAD-seasonal affective disorder, sexual behaviour
